Cross-Country Fault Example - GE D90 Plus Instruction Manual

SINGLE-POLE TRIPPING

Cross-country fault example

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This enhanced operation of the pilot-aided schemes is the reason to use a short pilot
scheme priority time when setting the trip output logic. The timer will force the scheme to
wait for a decision from the pilot scheme for a short period of time before accepting any
local trip request. The advantage, however, materializes only if two-bit or four-bit
communications channels are used, and is important only on parallel lines or when the
application requires maximum accuracy of single-pole tripping. In other cases, it is not
recommended to delay the local trip decision.
Assume a single-pole operation application where D90
terminal line (terminals T1 and T2) using phase and ground distance zone 1, 2 and 3
elements in a permissive overreaching transfer trip scheme. The performance of the
system with one-bit, two-bit, and four-bit communications channels is outlined for a mid-
line phase A-to-ground fault and a coincident phase B-to-ground fault just behind terminal
T2. Assume also that the reclosers are enabled and reset.
The following protection elements will pickup at terminal T1.
• Ground distance zone 1, 2, and 3 for an AG fault.
• Ground distance zone 2 and 3 for a BG fault.
• Phase distance zone 2 and 3 for an AB fault.
The phase selector will determine the fault is type ABG at terminal T1. This response is
independent from the distance elements; the phase selector sees two forward faults.
The following protection elements will pickup at terminal T2.
• Ground distance zone 1, 2, and 3 for an AG fault.
The phase selector will determine the fault is type AG at terminal T2. The reverse BG fault is
likely to be ignored.
If a one-bit channel is used, terminal T1 will trip three poles but terminal T2 will trip phase A
only (see the table below) which is undesirable.
Table 48: Trip table for cross-country fault example, one-bit channel
Terminal Remote data
Bit pattern
RX1
T1 1
T2 1
If a two-bit channel is used, both terminal T1 and T2 will trip phase A only (see the table
below) which is the desired outcome.
Table 49: Trip table for cross-country fault example, two-bit channel
Terminal Remote data
Bit pattern
RX1 RX2
T1 1 0
T2 1 1
If a four-bit channel is used, both terminal T1 and T2 will trip phase A only (see the table
below) which is the desired outcome.
Plus
Local data
Remote Local determination
determination of fault of fault type
type
Any MULTI-P (ABG)
Any AG
Local data
Remote Local determination
determination of fault of fault type
type
AG ABG
ABG AG
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 15: THEORY OF OPERATION
IEDs are used to protect a two-
Trip output
TRIP 3-POLE
TRIP PHASE A
Trip output
TRIP PHASE A
TRIP PHASE A